Present condition of LPG national stockpiling as main part's underground cavern of water sealing system

Japan National Oil Corporation (JNOC) is preparing to construct national LPG stockpiling bases (Nanao, Ishikawa prefecture; Fukushima, Nagasaki prefecture; Namikata, Ehime prefecture; Kurashiki, Okayama prefecture) for achievement of a government LPG stockpile of 1.5 million tons by fiscal 2010. JNOC has also conducted a feasibility study at Kamisu site (Ibaraki prefecture). As stockpiling systems, on-ground tanks system and water-sealed underground tanks system will be adopted. Underground tanks system will be adopted at stockpiling bases in Namikata (450 thousand tons) and Kurashiki (400 thousand tons). Underground stockpiling facilities which are build by creating caverns and then sealing normal temperature LPG inside by means of groundwater pressure. This methods is used at many different bases in overseas because of it has a high level of safety, and is economical to construction and maintain. In this paper, outline of each project, principle and characteristic of underground cavern stockpiling method, and design of water sealing system are described.